Conserving and Rebuilding Soils

The literature on soil erosion contains countless references to the “loss of protective vegetation.” Over the last half-century, clearcutting, overgrazing, and overplowing have removed so much of that protective cover that the world is quickly losing soil accumulated over long stretches of geological time (see “Civilization’s Foundation Eroding”). Preserving the biological productivity of highly erodible cropland depends on planting it in grass or trees before it becomes wasteland.

The 1930s Dust Bowl that threatened to turn the U.S. Great Plains into a vast desert was a traumatic experience that led to revolutionary changes in American agricultural practices, including the planting of tree shelterbelts (rows of trees planted beside fields to slow wind and thus reduce wind erosion) and strip cropping (the planting of wheat on alternate strips with fallowed land each year). Strip cropping permits soil moisture to accumulate on the fallowed strips, while the alternating planted strips reduce wind speed and hence erosion on the idled land.

Soil Conservation Legislation

In 1985, the U.S. Congress, with strong support from the environmental community, created the Conservation Reserve Program (CRP) to reduce soil erosion and control overproduction of basic commodities. By 1990 there were some 14 million hectares (35 million acres) of highly erodible land with permanent vegetative cover under 10-year contracts. Under this program, farmers were paid to plant fragile cropland to grass or trees. The retirement of those 14 million hectares under the CRP, together with the use of conservation practices on 37 percent of all cropland, reduced U.S. soil erosion from 3.1 billion tons to 1.9 billion tons between 1982 and 1997. The U.S. approach offers a model for the rest of the world.

Conservation Tillage

Another tool in the soil conservation toolkit—and a relatively new one—is conservation tillage, which includes both no-till and minimum tillage. Instead of the traditional cultural practices of plowing land and discing or harrowing it to prepare the seedbed, and then using a mechanical cultivator to control weeds in row crops, farmers simply drill seeds directly through crop residues into undisturbed soil, controlling weeds with herbicides. The only soil disturbance is the narrow slit in the soil surface where the seeds are inserted, leaving the remainder of the soil undisturbed, covered by crop residues and thus resistant to both water and wind erosion. In addition to reducing erosion, this practice retains water, raises soil carbon content, and greatly reduces energy use for tillage.

In the United States, where farmers during the 1990s were required to implement a soil conservation plan on erodible cropland in order to be eligible for commodity price supports, the no-till area went from 7 million hectares in 1990 to 27 million hectares (67 million acres) in 2007. Now widely used in the production of corn and soybeans, no-till has spread rapidly in the western hemisphere, covering 26 million hectares in Brazil, 20 million hectares in Argentina, and 13 million in Canada. Australia, with 12 million hectares, rounds out the five leading no-till countries.

Once farmers master the practice of no-till, its use can spread rapidly, particularly if governments provide economic incentives or require farm soil conservation plans for farmers to be eligible for crop subsidies.

Farming practices that reduce soil erosion and raise cropland productivity usually also lead to higher carbon content in the soil. Among these are the shift to minimum-till and no-till farming, the more extensive use of cover crops, the return of livestock and poultry manure to the land, expansion of irrigated area, a return to more mixed crop-livestock farming, and the forestation of marginal land.

International Soil Conservation Efforts

Other approaches are being used to halt soil erosion and desert encroachment on cropland. In July 2005, the Moroccan government, responding to severe drought, announced that it was allocating $778 million to canceling farmers’ debts and converting cereal-planted areas into less vulnerable olive and fruit orchards.

Countries south of the Sahara are concerned about the growing displacement of people as grasslands and croplands turn to desert. As a result, the African Union has launched the Green Wall Sahara Initiative. This plan, originally proposed by Olusegun Obasanjo when he was president of Nigeria, calls for planting 300 million trees on 3 million hectares in a long band stretching across Africa. Senegal, which is currently losing 50,000 hectares of productive land each year, would anchor the green wall on the western end. Senegal’s Environment Minister Modou Fada Diagne says, “Instead of waiting for the desert to come to us, we need to attack it.” Since the initiative was launched, its scope has broadened to include improved land management practices such as rotational grazing.

China is likewise planting a belt of trees to protect land from the expanding Gobi Desert. This green wall, a modern version of the Great Wall, is projected to extend some 4,480 kilometers (2,800 miles), stretching from outer Beijing through Inner Mongolia (Nei Monggol). In addition to its Great Green Wall, China is paying farmers in the threatened provinces to plant their cropland in trees. The goal was to plant trees on 10 million hectares, easily one tenth of China’s current grainland area, but recent pressures to expand food production appear to have slowed this tree planting initiative.

In Inner Mongolia, efforts to halt the advancing desert and to reclaim the land for productive uses rely on planting desert shrubs to stabilize the sand dunes. And in many situations, sheep and goats have been banned entirely. In Helin County, south of the provincial capital of Hohhot, the planting of desert shrubs on abandoned cropland has now stabilized the soil on the county’s first 7,000-hectare reclamation plot. Based on this success, the reclamation effort is being expanded.

The Helin County strategy centers on replacing the large number of sheep and goats with dairy cattle. The dairy herds are kept within restricted areas, feeding on cornstalks, wheat straw, and the harvest from a drought-tolerant forage crop that is used to reclaim land from the desert. Local officials estimate that this program will double incomes within the county during this decade.

To relieve pressure on China’s rangelands as a whole, Beijing is asking herders to reduce their flocks of sheep and goats by 40 percent. But in communities where wealth is measured in livestock numbers and where most families are living in poverty, such cuts are not easy or, indeed, likely, unless alternative livelihoods are offered to pastoralists along the lines proposed in Helin County.

Soil Conservation Conclusions

In the end, the only viable way to eliminate overgrazing on the two fifths of the earth’s land surface classified as rangelands is to reduce the size of flocks and herds. Not only do the excessive numbers of cattle, and particularly sheep and goats, remove the vegetation, but their hoofs pulverize the protective crust of soil that is formed by rainfall and that naturally checks wind erosion. In some situations, the preferred option is to keep the animals in restricted areas, bringing the forage to them. India, which has successfully adopted this practice for its thriving dairy industry, is the model for other countries.

Protecting the earth’s soil also warrants a worldwide ban on the clearcutting of forests in favor of selective harvesting, simply because with each successive clearcut there are heavy soil losses until the forest regenerates. And with each subsequent cutting, more soil is lost and productivity declines further.

Together, restoring the earth’s tree and grass cover and practicing conservation agriculture protect soil from erosion and reduce flooding. They also sequester carbon, making them powerful tools in the effort to fight global warming.

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